Separators for separating solid matter from a fluid are known from the prior art. In particular, separators having a cyclone structure are known which employ the specific function of a rotating flow of fluid in order to separate solid matter based on inertia forces due to differences in density. According to the known separators using a cyclone structure, a problem arises in cases where the flow rate of treated fluid varies in wide ranges. In particular, in cases where the fluid to be treated enters the cyclone structure as flush, the function for separating solid matter from the fluid cannot be secured.